1. Field of the Invention
This invention relates to a method for removing solid sulfur deposited in petroleum bearing formations, oil wells, flowlines, etc., and more particularly to a method for enhancing the rate at which dialkyl disulfides dissolve solid sulfur.
2. Description of the Prior Art
The problem of sulfur accumulating in sour gas and distillate wells to plug the flow of fluids therefrom is well-known. U.S. Pat. No. 3,846,311 which was issued to two of the present inventors on Nov. 5, 1974, discusses this problem and various methods which have been used to remove the solid sulfur. As disclosed in this patent, the dialkyl disulfide sulfur solvents have a number of advantages over carbon disulfide which has been and is still used as a sulfur solvent in well applications. The patent teaches a method for increasing the amount of sulfur which a given quantity of a dialkyl disulfide solvent will dissolve with the ratio of sulfur to solvent being as high as five to one on a weight basis at high temperature. The method taught by the patent requires that the disulfide be catalyzed by addition of a small amount of aliphatic amine followed by an aging process. While the solvent produced in accordance with this reference exhibits an outstanding capability to dissolve several times its weight of sulfur, a period of at least 10 to 5 days at elevated temperature is required to obtain such material. If the reaction is allowed to take place at room temperature, e.g., 75.degree. F., a period of at least 30 days is required, necessitating large storage volumes where the solvent is being manufactured and used on a commercial scale. Also taught in the patent at column 4 lines 26 through 30 is the fact that the aged catalyzed disulfide solution is initially slow in sulfur dissolving rate but increases after a small percentage of sulfur is dissolved in the solution.
U.S. Pat. No. 3,531,160 issued to Fisher on Sept. 29, 1970, also illustrates the use of alkyl disulfides (not catalyzed) in the removal of sulfur from wells. Fisher teaches that "sulfur reacted disulfide" has a higher capacity for dissolving sulfur than the other solvents listed in the patent. The total solvent capacity of this material for sulfur is listed as 15.5 pounds per barrel of solvent at 75.degree. F.
It is apparent that the rate of sulfur dissolution is important in applications where the sulfur solvent is flowed through tubing to remove sulfur deposited on the inner surfaces of the well tubing. If the dissolution rate is slow, then either a larger amount of solvent has to be used or it must be flowed through the tubing very slowly to allow sufficient contact time with the sulfur. In a normal process, the solvent is also pumped a short distance out into the producing formation and allowed to soak for a time to remove sulfur deposited within the pore space of the formation. The well must be non-productive during this soaking period and for economic reasons it is therefore desirable to minimize the soaking period.